Method of producing probabilities of being a template shape

ABSTRACT

A method of identifying a printed page from a scan of the printed page is disclosed. The method comprises the steps of generating a page key of the printed page on the basis of the scan ( 710 ), searching a database ( 199 ) for a similar page key ( 730 ). For each found similar page key ( 740 ), the method further comprises; retrieving from the database an instance key location ( 750 ), generating an instance key for the printed page ( 530 ), based on the retrieved instance key location of the referenced page instance; and comparing the generated instance key for the printed page with the retrieved instance key of the referenced page instance ( 770 ). A match between the instance keys indicates that the printed page is the referenced page instance.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the right of priority under 35 U.S.C. §119 basedon Australian Patent Application No. 2008259730, filed Dec. 18, 2008,which is incorporated by reference herein in its entirety as if fullyset forth herein.

TECHNICAL FIELD

The current disclosure relates to a method for identifying a pageinstance of a source document from a scan of the page instance.

BACKGROUND

Printing and copying paper documents plays a central role in thedissemination of information in the office environment. Managing andmaintaining the organization of paper documents and their relationshipto their digital counterparts is becoming increasingly difficult due tothe explosion in the number of documents and the number of peoplesimultaneously working on them.

A number of methods of improving the management of this complexity existthat are based on maintaining a database of relationships betweendigital versions of a document and their paper representations. Whensuch a database exists, upon identifying a document, a copying devicemay query the database for the digital version of the document andexecute a number of different options based on the original descriptionof the document. Such options may include reprinting from the originalof the document or printing an updated version of the document, if suchhas been registered with the database.

One method of maintaining a database of the relationships betweendigital versions of a document and their paper representations is basedon printing a machine readable mark on the document, such as a bar code,that identifies the document that has been printed. This method has thedisadvantage that it requires special marks on the document. These markscan be visually distracting. In addition, the printing of such marks mayrequire special inks or papers, thereby increasing the cost of thesystem.

Another method of maintaining a database of the relationships betweendigital versions of a document and their paper representations is basedon image indexing. In this method, a distinct property of the documentis stored in the database. The property can be recovered from a scan orimage of the document and can distinguish the document from otherdocuments. The Fourier magnitude of a thumbnail of a document is a knownexample of such a property. One disadvantage of this method is that themethod cannot discriminate between documents that share similar imagecontent. Another disadvantage is that similar images can be confused, ifextraneous marks have been added to the document, either by annotation,or by wear and tear of the paper on which the document is printed.

A further method of maintaining a database of the relationships betweendigital versions of a document and their paper representations is basedon extracting a unique property of the medium on which the print isbeing made. An example of such a unique property is the image of thefibre structure of a section of the surface of the paper, or any otherprinting medium on which the document has been printed. A disadvantageof this method is that it requires a fixed portion of the document to beleft largely unprinted, thereby restricting the acceptable geometry ofthe source document. Such a restriction is displeasing to the user andreduces the utility of the method.

SUMMARY

According to a first aspect of the present disclosure, there is provideda method for identifying a printed page from a scan of the printed page.The method generates a page key of the printed page on the basis of thescan and sends the generated page key to a database to initiate a searchfor a similar page key. For each similar page key retrieved from thedatabase, the method then retrieves from the database an instance keylocation for a page instance with the respective similar page key,generates an instance key for the printed page, based on the retrievedinstance key location of the respective page instance, and sends thegenerated instance key for the printed page to the database forcomparison with an instance key of the respective page instance. A matchbetween the instance keys indicates that the printed page is therespective page instance.

According to a second aspect of the present disclosure, there isprovided method for identifying a page instance of a source documentfrom a scan of the page instance. The scan is obtained from a print ofthe page instance, with the print being effected by a printing device ona physical medium. The method is typically executed by a processed in acomputer and finds at least one image in a database that is similar tothe scanned image of the printed page instance. The similarity is basedon a first physical characteristic in the scan, the characteristic beingsubstantially invariant between different printed instances of thesource document. The method then, for each of the at least one similarimages, determines a location in the scan based on informationassociated with the respective similar image, obtains a secondcharacteristic from the scan, the second characteristics beingpositioned in said location, wherein the second characteristic issubstantially variant between different instances of said sourcedocument, and compares the second characteristic of the page instancewith a corresponding second characteristics of the respective similarimage. A match between the second characteristics indicates that therespective similar image is a source document for the printed pageinstance.

According to a third aspect of the present disclosure, there is provideda computer-system implemented method for identifying a printed page. Themethod scans a plurality of first printed pages to generate a first scanof each first printed page and the generates a page key and an instancekey for each first printed page on the basis of its respective firstscan. The generated page key and an instance key for each first page arethen stored in a database. An unidentified printed page is then scannedto generate a scan image of the unidentified page and, on the basis ofthe scan of the unidentified page, a page key of the unidentifiedprinted page is generated. The method then sends the generated page keyto a database to initiate a search for a similar page key to the pagekey of the unidentified page. For each retrieved similar page key, themethod then retrieves from the database an instance key location for afirst page with the respective similar page key, generates an instancekey for the unidentified printed page, based on the retrieved instancekey location of the respective first page, and sends the generatedinstance key for the unidentified printed page to the database forcomparison with an instance key of the respective first page. A matchbetween the instance keys indicates that the unidentified printed pageis identical to the respective first printed page.

According to further aspects of the present disclosure, there isprovided a system and a computer readable storage medium forimplementing any one of the aforementioned methods.

Other aspects of the invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

At least one embodiment of the present invention will now be describedwith reference to the drawings, in which:

FIGS. 1A and 1B show a schematic block diagram of a digital photocopyingsystem upon which at least some of the steps of the described method foridentifying a printed page from a scan of the printed page can bepracticed;

FIG. 2 shows a document with multiple pages, multiple prints andmultiple versions;

FIG. 3 shows changes of the location of an instance key betweendifferent versions of a given document;

FIG. 4 shows a method of adding a page data to a database;

FIG. 5 shows a method of generating page keys from a scan of a printedpage;

FIG. 6 shows reference data included in an entry in a document databasefor a single document;

FIG. 7 is a block diagram of the method of identifying a printed pagefrom a scan of the printed page;

FIG. 8 is a block diagram showing a method of generating a page key froma scan of the page;

FIG. 9 shows a region of the Fourier transform of a down-sampled scanthat is used to generate a page key;

FIG. 10 is a block diagram showing a method of determining an instancekey location from a scan; and

FIG. 11 is a block diagram showing a method of generating an instancekey based on the instance key location on a scan.

DETAILED DESCRIPTION INCLUDING BEST MODE

It is to be noted that any discussions relating to prior artarrangements relate to discussions of documents or devices which formpublic knowledge through their respective publication and/or use. Suchshould not be interpreted as a representation by the present inventor(s)or the patent applicant that such documents or devices in any way formpart of the common general knowledge in the art.

A method for identifying a printed page from a scan of the page will bedisclosed below with reference to FIGS. 1 to 11. In more generic terms,the describe method is also a method for identifying a printed instanceof a source document from a scan of the printed instance. The method isdescribed in terms of an office workflow environment, however otherconfigurations and arrangements are also possible and some of these willbe noted throughout the description.

FIGS. 1A and 1B collectively form a schematic block diagram of aphotocopying system 100, upon which the disclosed method and otherrelated methods can be practiced. The digital photocopying system 100 isused to print documents and register the documents in an associateddatabase 199, as seen in FIG. 1A.

As shown in FIG. 1A, the photocopying system 100 is formed by a computermodule 101, input devices such as a keypad 102, a mouse pointer device103 (optional). A scanning module 126 is used for receiving paper asinput and for digitising any images formed on the paper into anelectronic format. Photocopying system 100 also includes output devicessuch as an LCD display device 114 and a printer 115. Notably, thephotocopying system 100 can operate as a printer (including a networkedprinter), a scanner or a photocopier. In the printer operational mode,the photocopying system 100 uses printer 115 to print documents withoutscanning them first. The metadata for the printed documents in this caseis obtained either from a local memory storage device (109 or 125) orfrom one of networks 122 or 120, via the respective interface 111 or108.

An output scanner module 127 is used for scanning the pages once theyare printed. The output scanner module 127 is not a standard option on adigital photocopier and represents an addition to the digitalphotocopier hardware that enables the described embodiment of thepresent method. This scanner 127 is positioned in the photocopyingsystem 100 at the output tray of the device and scans each page after ithas been printed, but before it has been provided to the user via theoutput tray. This scanner can be implemented in a variety of differentways. In the described embodiment of the present method the scanner is aContact Image Sensor (CIS) type scanner illuminated by a bank of LEDs.While in the described embodiment the scanner is integrated with theprinter, this is not strictly necessary for the execution of the presentmethod, and it would be possible for this output scanner to be aseparate device. Alternatively, a user may take the output of aprinter/digital photocopier and place it on the standard scannerintegrated with the digital photocopier.

An external Modulator-Demodulator (Modem) transceiver device 116 may beused by the computer module 101 for communicating to and from acommunications network 120 via a connection 121. The network 120 may bea wide-area network (WAN), such as the Internet or a private WAN. Wherethe connection 121 is a telephone line, the modem 116 may be atraditional “dial-up” modem. Alternatively, where the connection 121 isa high capacity (eg: cable) connection, the modem 116 may be a broadbandmodem. A wireless modem may also be used for wireless connection to thenetwork 120.

The computer module 101 typically includes at least one processor unit105, and a memory unit 106, for example formed from semiconductor randomaccess memory (RAM) and semiconductor read only memory (ROM). The module101 also includes an number of input/output (I/O) interfaces includingan audio-video interface 107 that couples to the video display 114,optional loudspeakers and microphone, an I/O interface 113 for thekeypad 102, optional mouse 103 and an interface 108 for the externalmodem 116 and printer 115. In some implementations, the modem 116 may beincorporated within the computer module 101, for example within theinterface 108. The computer module 101 also has a local networkinterface 111 which, via a connection 123, permits coupling of thephotocopying system 100 to a local computer network 122, known as aLocal Area Network (LAN). As also illustrated, the local network 122 mayalso couple to the wide network 120 via a connection 124, which wouldtypically include a so-called “firewall” device or device of similarfunctionality. The interface 111 may be formed by an Ethernet™ circuitcard, a Bluetooth™ wireless arrangement or an IEEE 802.11 wirelessarrangement.

The interfaces 108 and 113 may afford either or both of serial andparallel connectivity, the former typically being implemented accordingto the Universal Serial Bus (USB) standards and having corresponding USBconnectors (not illustrated). Storage devices 109 can also be provided,such as a hard disk drive (HDD) 110. Other storage devices may also beprovided, such as a floppy disk drive and a magnetic tape drive (notillustrated), as well as an optical disk drive 112. Portable memorydevices, such optical disks (eg: CD-ROM, DVD), USB-RAM, and floppy disksfor example may then be used as appropriate sources of data to thephotocopying system 100.

The components 105 to 113 of the computer module 101 typicallycommunicate via an interconnected bus 104 in a manner similar to aconventional mode of operation of a standard computer system known tothose in the relevant art.

The described methods may be implemented using the photocopying system100. In particular, the methods of FIGS. 4, 5, 7, 8, 10 and 11, to bedescribed, may be implemented as one or more software applicationprograms 133 executable within the computer module 101. In particular,the various disclosed steps and methods are effected by instructions 131in the software 133 that are carried out within the computer module 101.The software instructions 131 may be formed as one or more code modules,each for performing one or more particular tasks. The software may alsobe divided into two separate parts, in which a first part and thecorresponding code modules performs the various steps and methods and asecond part and the corresponding code modules manage a user interfacebetween the first part and the user.

The software 133 is generally loaded into the computer module 101 from acomputer readable medium, and is then typically stored in the HDD 110,as illustrated in FIG. 1A, or the memory 106. After loading, thesoftware 133 can be executed by the computer module 101. In someinstances, the application programs 133 may be supplied to the userencoded on one or more CD-ROM 125 and read via the corresponding drive112 prior to storage in the memory 110 or 106. Alternatively thesoftware 133 may be read by the photocopying system 100 from thenetworks 120 or 122 or loaded into the computer module 101 from othercomputer readable media. Computer readable storage media refers to anystorage medium that participates in providing instructions and/or datato the computer system 100 for execution and/or processing. Examples ofsuch storage media include floppy disks, magnetic tape, CD-ROM, a harddisk drive, a ROM or integrated circuit, USB memory, a magneto-opticaldisk, or a computer readable card such as a PCMCIA card and the like,whether or not such devices are internal or external of the computermodule 101. Examples of computer readable transmission media that mayalso participate in the provision of software, application programs,instructions and/or data to the computer module 101 include radio orinfra-red transmission channels as well as a network connection toanother computer or networked device, and the Internet or Intranetsincluding e-mail transmissions and information recorded on Websites andthe like.

The second part of the application programs 133 and the correspondingcode modules mentioned above may be executed to implement one or moregraphical user interfaces (GUIs) to be rendered or otherwise representedupon the display 114. Through manipulation of typically the keyboard 102and the mouse 103, a user of the photocopying system 100 and theapplication may manipulate the interface in a functionally adaptablemanner to provide controlling commands and/or input to the applicationsassociated with the GUI(s). Other forms of functionally adaptable userinterfaces may also be implemented, such as an audio interface utilizingspeech prompts output via the loudspeakers 117 and user voice commandsinput via the microphone 180.

FIG. 1B is a detailed schematic block diagram of the processor 105 and a“memory” 134. The memory 134 represents a logical aggregation of all thememory devices (including the HDD 110 and semiconductor memory 106) thatcan be accessed by the computer module 101 in FIG. 1A.

When the computer module 101 is initially powered up, a power-onself-test (POST) program 150 executes. The POST program 150 is typicallystored in a ROM 149 of the semiconductor memory 106. A programpermanently stored in a hardware device such as the ROM 149 is sometimesreferred to as firmware. The POST program 150 examines hardware withinthe computer module 101 to ensure proper functioning, and typicallychecks the processor 105, the memory (109, 106), and a basicinput-output systems software (BIOS) module 151, also typically storedin the ROM 149, for correct operation. Once the POST program 150 has runsuccessfully, the BIOS 151 activates the hard disk drive 110. Activationof the hard disk drive 110 causes a bootstrap loader program 152 that isresident on the hard disk drive 110 to execute via the processor 105.This loads an operating system 153 into the RAM memory 106 upon whichthe operating system 153 commences operation. The operating system 153is a system level application, executable by the processor 105, tofulfil various high level functions, including processor management,memory management, device management, storage management, softwareapplication interface, and generic user interface.

The operating system 153 manages the memory (109, 106) in order toensure that each process or application running on the computer module101 has sufficient memory in which to execute without colliding withmemory allocated to another process. Furthermore, the different types ofmemory available in the system 100 must be used properly so that eachprocess can run effectively. Accordingly, the aggregated memory 134 isnot intended to illustrate how particular segments of memory areallocated (unless otherwise stated), but rather to provide a generalview of the memory accessible by the computer module 101 and how such isused.

The processor 105 includes a number of functional modules including acontrol unit 139, an arithmetic logic unit (ALU) 140, and a local orinternal memory 148, sometimes called a cache memory. The cache memory148 typically includes a number of storage registers 144-146 in aregister section. One or more internal buses 141 functionallyinterconnect these functional modules. The processor 105 typically alsohas one or more interfaces 142 for communicating with external devicesvia the system bus 104, using a connection 118.

The application program 133 includes a sequence of instructions 131 thatmay include conditional branch and loop instructions. The program 133may also include data 132 which is used in execution of the program 133.The instructions 131 and the data 132 are stored in memory locations128-130 and 135-137 respectively. Depending upon the relative size ofthe instructions 231 and the memory locations 128-130, a particularinstruction may be stored in a single memory location as depicted by theinstruction shown in the memory location 130. Alternately, aninstruction may be segmented into a number of parts each of which isstored in a separate memory location, as depicted by the instructionsegments shown in the memory locations 128-129.

In general, the processor 105 is given a set of instructions which areexecuted therein. The processor 105 then waits for a subsequent input,to which it reacts to by executing another set of instructions. Eachinput may be provided from one or more of a number of sources, includingdata generated by one or more of the input devices 102, 103, datareceived from an external source across one of the networks 120, 122,data retrieved from one of the storage devices 106, 109 or dataretrieved from a storage medium 125 inserted into the correspondingreader 112. The execution of a set of the instructions may in some casesresult in output of data. Execution may also involve storing data orvariables to the memory 134.

The disclosed data processing arrangements use input variables 154 thatare stored in the memory 134 in corresponding memory locations 155-158.The data processing arrangements produce output variables 161 that arestored in the memory 134 in corresponding memory locations 162-165.Intermediate variables may be stored in memory locations 159, 160, 166and 167.

The register section 144-146, the arithmetic logic unit (ALU) 140, andthe control unit 139 of the processor 105 work together to performsequences of micro-operations needed to perform “fetch, decode, andexecute” cycles for every instruction in the instruction set making upthe program 133. Each fetch, decode, and execute cycle comprises:

(a) a fetch operation, which fetches or reads an instruction 131 from amemory location 128;

(b) a decode operation in which the control unit 139 determines whichinstruction has been fetched; and

(c) an execute operation in which the control unit 139 and/or the ALU140 execute the instruction.

Thereafter, a further fetch, decode, and execute cycle for the nextinstruction may be executed, Similarly, a store cycle may be performedby which the control unit 139 stores or writes a value to a memorylocation 132.

Each step in the methods of FIGS. 4, 5, 7, 8, 10 and 11 is associatedwith one or more segments of the program 133, and is performed by theregister section 144-147, the ALU 140, and the control unit 139 in theprocessor 105 working together to perform the fetch, decode, and executecycles for every instruction in the instruction set for the notedsegments of the program 133.

Alternatively, the currently disclosed method of identifying a printedinstance of a source document from a scan of the printed instance mayalso be implemented in a general-type computer system. Examples ofcomputers on which the described arrangements can be practised includeIBM-PC's and compatibles, Sun Sparcstations, Apple Mac™ or alikecomputer systems evolved therefrom. The disclosed methods can also beperformed on a dedicated hardware such as one or more integratedcircuits performing the functions or sub functions of the abovedescribed arrangements. Such dedicated hardware may include graphicprocessors, digital signal processors, or one or more microprocessorsand associated memories.

Having at their disposal the above described photocopying system 100, auser can print a document 117 by using the printer mode of thephotocopying system 100. Before reaching the user, the printed document117 is scanned by output scanner 127. This allows an electronic copy ofthe printed document 117 and a set of page keys (not shown) to begenerated on the basis of the scan of the printed document 117. Thedocument and the keys are then stored into a document database 199associated with the system 100. It is possible for the document database199 to be configured to run internally to the digital photocopyingsystem 100. However, in the described embodiment, the document database199 is implemented either on the local area network 122 or the wide areanetwork 120, to which the photocopying system 100 has access.

The keys that are stored in the database 199 together with a copy of thedocument, are used for indexing each document 117. A combination of twokeys is used. One key, referred to as a document page key, is generatedon the basis of a spatial arrangement of printed marks, or a physicalcharacteristic, that is captured by the scan and is usuallyrepresentative of the content of the document. As such the page key issubstantially invariant between different printed instances of thesource document. Another key, known as the instance key, is generatedeither from the spatial arrangement of printed marks that varysubstantially from print to print of the same document, or from aproperty of the print medium that varies substantially between each pageof the medium. As such the instance key is substantially variant betweendifferent printed instances of the source document. Details of thevarious key generation methods are given further in the text.

The keys are used to identify a printed document when, at a later time,a user attempts to photocopy the document on a digital photocopyingsystem, which may be the same or a different system from photocopyingsystem 100. The respective photocopying system queries the documentdatabase 199 for information associated with the original print of thedocument. Once a document is identified, various options for copying arepresented to the user based on the information retrieved from thedocument database.

To distinguish the different stages of the printed document lifecycle,some nomenclature is introduced with reference to FIG. 2. A document 210consists of pages 220, which are logically related according to somepurpose of the user. Typically, within a computer, a document will berelated to a single source file. This is not always the case, as a usermay sometimes merge two files together to make a third, with theintention of printing them as a single document, or may make a mergeddocument, tailoring the document according to its recipient and thelike. Documents may have several versions 230 of the same document.These revisions may be minor, such as changes in grammar, spelling or afraction of the text. Alternatively, the revisions may be major andinclude substantial rewriting of the text of the document.

When a document is printed onto a physical medium, an instance of a pageof a document 240 is created. Two instances may have the same logicalcontent, i.e. they may contain the same content from the document, butthey may be printed at different times or on different printing devices.

The disclosed method allows obtaining a scan of an instance 240 of aprinted page and determining from which page 220, from which version 230and of which document 210, the instance 240 was generated.

The difficulty of this task is illustrated with respect to FIG. 3. Here,six instances 301 to 306 are printed from the pages of a two-pagedocument, which has two versions. The first four instances 301 to 304originate from two prints of the first version of the document. The lasttwo instances 305 and 306 come from a print of the second version of thedocument. In this case, the first page of the document in version 1 andversion 2 are identical in content. Based on the information from thedocument printed on each of the instances, the first pages 301, 303 and305 of the prints will be considered identical as they come from thesame digital data. The first two instances 302 and 304 of the secondpage will be considered identical, and the third instance 306 of thesecond page will be determined to come from the second version of thedocument as the content is distinct from the content of the second pageof version 1. Based on just the information from the document printed onthe third instance of the first page, it is impossible to determine thatthis page is part of the second version of the document.

To resolve this ambiguity, it is possible to look at properties thatchange from instance to instance of either the medium, on which theprint is made, or of the print itself.

One example of a characteristic medium property is the fibre structureor the surface structure of the medium on which the instance is printed.Typically, these structures are highly unique to a local region of themedium and effectively distinguish each local area of each sheet ofmedia. However, to examine this structure that varies from instance toinstance, it is important that the particular section of the medium isnot printed over. Given that a print may consist of large patches ofsolid colour that are arbitrarily located on the page, it is impossibleto assume that the area of the medium to be examined will be located inthe same position from print to print. If such an assumption is made,then it is necessary that the user does not print on that region in anydocument that is to be used with this system. This limits the utility ofdocument indexing systems.

A second property that changes between printing instances is themicroscopic variation of the distribution of the colorant used in theprinting process, i.e. the toner in an electro-photographic printer orink in an inkjet printer. In an electro-photographic printer, toner isdeposited as a result of a number of physical processes that are subjectto substantial noise or turbulence, such as toner transfer betweendifferent surfaces in the machine. This leads to small variations of thetoner placement that are unique to each printout, even though theoverall visual impression of two prints of the same material can bealmost identical. Such variations are useful for discriminating betweendifferent instances of the same page. However, yet again, the area ofthe page that is best suited for use for discriminating between similarinstances, is dependent on the document content.

To illustrate the document content dependence of the positions betweeninstance discriminating information, a number of patches (not shown)have been identified in each page instance shown in FIG. 3. Thesepatches are selected as regions that have characteristic variations thatdiffer between instances and are positioned at what is known as theinstance key location 310 of each particular page of a particularversion of a document. So, for the first page in both versions of thedocument the instance key location 310 is in the lower right corner ofthe page. For the second page of the first version of the document, theinstance key location 310 is in the top right corner of the page, andfor the second page of the second version of the document, the instancekey location 310 is in the top left corner of the document.

FIG. 4 shows a flow diagram of the method 400 of adding document data todatabase 199. The method 400 is executed when the user first prints adocument and the document is added to the document database 199. Themethod starts with step 410, in which a job to be printed is sent to thedigital photocopying system 100. The printing job is typically in theform of a page description language (PDL), such as Postscript™ or PDF.The processor 105 of the digital copier 100 is configured to render thisdocument to a raster representation according to the instructions in thePDL. This is generally done on a page by page basis, so after step 410the method enters a loop over each page in the document. For the page ofthe PDL currently being printed, in step 420, the processor 105generates the raster representation used to drive the printingmechanism. In step 430, processor 105 drives printer 115 to print therespective page from this raster representation. In step 440, as theprinted page exits the digital photocopying system, processor 105 drivesoutput scanner 127 to scan the printed page. The output scanner 127generates the image data which is used in step 450 by processor 105 forthe generation of the two page keys, the document page key and theinstance key. At stage 455, the processor 105 verifies if there are morepages to be printed. If this is the case—the method 400 returns back andperforms step 420 with respect to the next page. If there are not morepages to be printed, the page keys and associated document metadata arestored in the database 199, in step 460.

In this described embodiment, the generated data that is stored in thedatabase 199 in step 460, is related to pages that are printed locallyby the photocopying system 100. However, this does not have to be thecase and pages that are not printed locally can also be added to thedatabase 199, In this case the method 400 would start at step 440 andproceed to scan more pages, as indicated with the dotted loop line.

The step 450 of generating the page keys from a scan of a printed pageis now described in more detail with reference to FIG. 5. In the firststep 510 of this method 450, processor 105 generates a document pagekey. In the described embodiment, the page key is obtained from the scandata, but it may also be generated from the original PDL, from therendered raster representation of the page, or from any combination ofthe three. Next, in step 520, the scan data will be analysed byprocessor 105 to determine which region of the scan will be used forgeneration of the instance key. This region is called the instance keylocation 310. Again, in an alternative embodiment, instead of the scandata, the original PDL or the rendered raster representation of the pagemay be used to determine the instance key location. Similarly to thedocument page key, any combination of the above (the scan data, theoriginal PDL and the rendered raster representation of the page), mayalso be used to determine the instance key location. Finally, in step530, processor 105 generates the instance key from the scan data relatedto the instance key location. Steps 510 to 530 will be described in moredetail further in the text.

The precise information that is stored in the database 199 in step 460is application dependent. The reference data included in a single recordentry in the document database 199, according to the describedembodiment, is illustrated by FIG. 6. Thus, FIG. 6 represents a singlerecord representing a particular document in the database 199. Thedocument ID represents a unique identifier associated with eachdocument. This identifier is linked to metadata that is related to theoriginal document and is used to generate the printed document: datarepresenting the location of the original document (Original Location),data representing the owner of the original document (Original Owner),and data representing the location of the original PDL (Original PDL).Other information, such as versioning information, may also be storedhere. However, such information can generally be determined directlyfrom the original document. In addition to these meta-data entries, thepage keys corresponding to each of the pages that comprise the documentare also stored. This page data consists of an entry for each pageincluding the document page key, the instance key location and theinstance key. Thus, the illustrated document data comprises referencesto, as well as the associated page key information of the instances ofeach page included in the document. Of course this information can bestructured in different ways. For example, each page can be referencedindependently from the document it is included in. In addition, thereference data shown in FIG. 6 can be split into two. For instance, theinstance key location and the instance key can be saved in a separatelocation, with the document data in FIG. 6 only including reference totheir location. Each of these records can be stored in the database 199,which in the described embodiment is a relational database, such as anSQLlite database. Such database can be searched according to differentfields in the database entry and allows retrieval of associated records.The searching mechanism for the database depends on the detailed natureof the document page keys and the instance keys.

The method 700 of identifying a printed page from a scan of the printedpage is shown in FIG. 7. Using the scan of the unidentified printedpage, effected on the digital photocopying system 100, the method 700retrieves from the document database 199 a source document correspondingto the printed page, thus identifying the page.

The method 700 starts with step 710, in which the user places a documentto be retrieved on the scanner of the photocopying system 100 and a scanis performed. It should, however, be noted that the scan does not haveto be performed locally on photocopying system 100. Instead the scanindicated with step 710 may be performed on a separate, either local orremote, system, and the scan data forwarded or stored in database 199,or at different location, for processing. For this reason the step 710is indicated with dotted line in FIG. 7.

The processor 105 uses the scan data obtained from scanning unit 126 to,in step 510, generate a document page key. In step 730, the processor105 sends the generated document page key, via interface 108 or 111, tothe document database 199, where a search is initiated for similar pagekeys. As a result of the performed search, a list of one or more pageswith similar page keys is generated by the database 199. The degree ofsimilarity depends of the type of key being used and will be describedlater in the text.

The document database 199 returns the pages, or the references to thepages, corresponding to the ten most similar document keys. At step 740the processor 105 starts a loop that considers, in turn, each similarpage or reference thereof, returned by the document database. In step750, the processor 105 retrieves an instance key location of therespective similar page from the database 199. In step 530, theprocessor 105 uses the retrieved instance key location and the scan datafrom the printed page to generate an instance key for the scannedprinted page. In step 770, the processor 105 sends this generatedinstance key to document database 199, where it is compared with theinstance key of the respective page being processed by the loop.Alternatively, the instance key of the respective “similar” page can beretrieved from the database and compared with the instance key generatedfor the printed page by processor 105.

The choice of comparison method depends on the nature of the instancekey and will be described later in the text. If the instance keys match,this indicates that the printed page is an instance of the respectivepage found on the database. In this case, the method may continue withan optional step 780, in which the metadata corresponding to theoriginal document is retrieved from the document database.

Once the metadata of the matching document has been retrieved then anumber of options may be presented to the user. These options includebut are not limited to:

(i) reprinting from the original;

(ii) printing the latest version of the document, if different versionsexist;

(iii) display of the document owner, creation date or other metadata;

(iv) display of the copy history of the document; or

(v) emailing or otherwise transferring the original document file to theuser.

Alternatively, the data of the match can be used for other purposes,such as monitoring and statistics.

These options represent a substantial advantage over known prior artmethods. For example, the present method can discriminate between boththe document and the instance level simultaneously, without makingrestrictions on the format of the users documents. In particular, bycombining the generality of image matching with the high reliability ofdocument instance matching, the present method ensures that incorrectidentification of documents is reduced.

If the instance keys do not match, and there are further similardocuments to consider, then the method returns to step 740. If there areno further similar documents to consider, then the method 700 endswithout finding the original document, corresponding to the scanneddocument, in the database.

Creating Document Image Key

The sub-method 510 of FIG. 5 will now be described in more detail withreference to FIG. 8. The input to this sub-method is a scan of a printinstance, such as the ones described in relation to steps 440 and 710.However, the input data may also be retrieved by way of a lookup fromthe database. Scan data is generally provided from a scanner interfaceas a set of ROB digital signals in raster order. The amount of data froma scanner, which typically operates at 600 dpi and has a width of around12 inches, is typically 140 MB per second, for a printer operating at 60pages per minute. Such a large amount of data must be substantiallyreduced to reduce the cost of the system and its operating time. So, thefirst step 810 in the sub-method 510 is for processor 105 to convert theinput RGB data to grey scale through the equation:

Y=0.299R+0.587G+0.114B.

In addition, the colour converted data is down-sampled to 300 dpi, then150 dpi, then 75 dpi, and then 37.5 dpi, by repeatedly convolving theimage data both horizontally and vertically with a 3 tap Burt-Adelsonfilter, as is commonly known in the art. The 300 dpi representation isstored for later extraction of the instance key related image data.Other methods of colour conversion and down-sampling may be applied withsimilar efficacy. This step reduces the size of a single A4 scan toaround 10 MB, uncompressed, for the 300 dpi data, and to an image ofaround 400 pixels by 300 pixels, for the 37.5 dpi version.

In the second step 820, the page is approximately located in the scan.This is typically done through a hardware-assisted process in thedigital copier's scanning subsystem. If the scanner is a sheet feedtype, then the leading edge of the paper is detected by an opticalsensor and is available to the copier firmware subsystem after a scan.If the scanner is a platen type, the paper position is often detectedusing a short pre-scan and again is available from the copier firmwaresubsystem.

In step 830, a 2D discrete Fourier transform of the rectangle enclosingthe image of the document (from the 37.5 dpi resolution version of thedocument) is performed using the Fast Fourier Transform. This results ina 350 by 280 pixel Fourier image, each pixel of which is represented bya complex number. A 16×8 block of Fourier coefficients with positivevertical frequencies closest to the image mean (which is the DC value)is identified, as represented diagrammatically in FIG. 9 for an imagesize of 350 by 280 pixels. In step 840, the magnitude of each complexFourier coefficient from that block is taken and used to, in step 850,form a 1D vector. It should be noted that the DC position of the FFT inFIG. 9 is located in the (175,140) pixel of the image. The formed 1Dvector represents the document page key.

Returning now to FIG. 7, step 730 is described here in more detail. Inthis step, the document database is searched to find images that aresimilar in content to the image of the scanned document instance. Todetermine a list of similar documents, document page keys must becompared and ranked according to a similarity measure. If two documentpage keys are denoted D_(i) ⁽¹⁾ and D_(i) ⁽²⁾ where the index ienumerates over the 128 elements of the document page key, then two keyscan be compared using normalised correlation:

$C = {\frac{\sum\limits_{i}\; {D_{i}^{(1)}D_{i}^{(2)}}}{\sqrt{\sum\limits_{i}\; D_{i}^{{(1)}^{2}}}\sqrt{\sum\limits_{i}\; D_{i}^{{(2)}^{2}}}}.}$

In the described embodiment, the document database compares the page keyof the document to be searched for, to each other document page key inthe database. As a result of this comparison, step 730 returns a list ofpossible matches that comprises the pages with the corresponding highestnormalised correlation score.

The method 510, discussed above with reference to FIG. 8, is used forgenerating the document page key. The method generates a vector of 128floating point numbers to represent each page of each document and canbe used to determine a similar page of a document regardless of the typeof content in the document, be it images, graphics or text. There are anumber of other possible ways of forming the document page key known inthe prior art, such as performing Optical Character Recognition (OCR) onthe text of the scan to determine salient words or phrases in thedocument, and using this collection of salient words as a document pagekey. Alternately, other image based methods such as Fourier-Mellindescriptors, or SIFT (Scale-Invariant Feature Transform) features mayalso be used.

Now the sub-method 520 of FIG. 5 is described in more detail withreference to FIG. 10. In general, determining where the instance keyshould be located on the page is done by finding the region of thescanned image with the highest luminance. This allows determining whicharea of the scanned image is mostly the medium on which the print hasbeen made. Such areas tend to have a large amount of random structuregenerated by the fibres of the print medium. Checking the gradiententropy of this region then determines if there is sufficient structurein this region to ensure good discrimination between instance keys inthe database. If there is not sufficient structure in the region, then asearch is carried out to find the region with the most structure andthat is used for the instance key location.

In the described embodiment, the instance key is based on a region ofthe scan of size 128×128, with a resolution of 300 dpi. With respect toFIG. 10, the first step 1010 in the sub-method 520 includes theprocessor 105 processing the data of the area of the 37.5 dpi documentgenerated in step 810. The area is contained within the boundaries ofthe document, as determined in step 820. The aim of the data processingin step 1010 is to determine which 16×16 block has the highest averageluminance value. In step 1020, the processor 105 calculates a measure ofthe gradient entropy of this block on corresponding pixels in the 300dpi image by first generating x and y gradient images over the blockusing:

d _(x)(i,j)=Y(i,j)−Y(i−1,j)

d _(y)(i,j)=Y(i,j)−Y(i,j−1)

If the luminance data is in the range 0 to 255, then the derivativesmust be between −255 and 255. Due to the down-sampling of the 600 dpiscan to 300 dpi, the range of the derivatives tends to be much smallerthan this. The gradient entropy measure is determined by forming twohistograms of the x and y derivatives:

${h_{x}(v)} = {\sum\limits_{i,j}\; {\delta \left( {{d_{x}\left( {i,i} \right)} - v} \right)}}$${h_{y}(v)} = {\sum\limits_{i,j}\; {\delta \left( {{d_{y}\left( {i,j} \right)} - v} \right)}}$

Normalising these forms probability distributions;

${p_{x}(v)} = \frac{h_{x}(v)}{\sum\limits_{v}\; {h_{x}(v)}}$${p_{y}(v)} = \frac{h_{y}(v)}{\sum\limits_{v}\; {h_{y}(v)}}$

The combined Shannon entropy of the two one-dimensional histograms cannow be calculated;

$E = {{\sum\limits_{v}{{p_{x}(v)}\log \; {p_{x}(v)}}} + {\sum\limits_{v}{{p_{y}(v)}\log \; {p_{y}(v)}}}}$

If the gradient entropy is larger than a fixed threshold, which in thedescribed embodiment, is 3.0, then the corresponding region of the 300dpi sub-sampled version of the scan is used as the instance key region.If the gradient entropy is not larger than the fixed threshold, then theprocessor 105 conducts a further search over the 37.5 dpi in step 1030to determine which 16×16 block has the highest gradient entropy. Thecorresponding region of the 300 dpi sub-sampled version of the scan withthe highest gradient entropy is used as the instance key region.

The calculation of the instance key in sub-method 530 of FIG. 5 is nowdescribed in more detail with reference to FIG. 11. In the first step1110 of this sub-method, the processor 105 effects a Discrete FourierTransform of the 128×128 instance key region identified in sub-method520 using the FFT. Next, in step 1120, the magnitude of the FFT isdetermined and the magnitude of the Fourier coefficients is taken. Instep 1130, the processor 105 calculates a raster order of the magnitudesof the FFT coefficients to form a 1 dimensional vector that representsthe instance key for this printed instance.

When two instance keys are of the type described above, a comparisonbetween these keys, such as the one referred to in step 770, is effectedin the following way. Let us denote the two instance keys as K_(i) ⁽¹⁾and K_(i) ⁽²⁾, where the index i enumerates over the 16384 elements ofthe instance key. Two keys are compared using normalised correlation:

$C = \frac{\sum\limits_{i}\; {K_{i}^{(1)}K_{i}^{(2)}}}{\sqrt{\sum\limits_{i}\; K_{i}^{{(1)}^{2}}}\sqrt{\sum\limits_{i}\; K_{i}^{{(2)}^{2}}}}$

Two keys are considered a match if their normalised correlation is abovea fixed threshold. In the described embodiment this threshold is 0.5.

The foregoing describes only some embodiments of the present invention,and modifications and/or changes can be made thereto without departingfrom the scope and spirit of the invention, the embodiments beingillustrative and not restrictive.

In the preceding description, both the document page keys and theinstance keys were generated from the Fourier magnitude of the scandata. Numerous other approaches and image transforms can also be used togenerate such keys, such as wavelet transforms, Walsh-Hadamardtransforms, Radon transforms and the like. Also, the describedimplementation determined the Fourier magnitudes using an FFT routine.In some implementations it may be preferable to calculate the Fouriercoefficients directly in the spatial domain, particularly if thealgorithm is embedded in a low-power computing device.

Another variation of the approach described above includes changing theresolution and sizes of the images that are being processed and the sizeof the stored document index keys. Also, the key comparison methods usedabove may be modified to use weighted sums of coefficients, or lineardiscriminant analysis, or principal component analysis to compress orspeed up the comparison sets.

A further variation on the described embodiment is to generate thedocument page key and/or the instance key from full colour data insteadof the Y colour component. This includes choosing a differentone-dimensional subspace of the colour data, which is morediscriminating for a given document. For instance one can calculate theprincipal components of the colours of a document and use the firstprincipal component as the colour channel for the creation of thedocument page key.

Many other methods can also be used to choose which area of the documentis to be used as the instance key. In the described embodiment, thisarea was chosen by either finding the highest luminance portion of thescan image or, if that was not bright enough, finding the area of thescan image with the largest gradient entropy. Other methods includeevaluating the standard deviation of the image area, evaluating theimage histogram entropy or evaluating the entropy of the image regionprojected onto random basis functions.

The present method has been described with reference to a single sidedprinting environment. However, the present method could also bepracticed in a duplex printing environment by including a duplex scannerinstead of a single scanner at the output stage of the printer.Similarly, the described embodiment did not take into account theability of modem printers to dynamically change the formatting ofdocuments before printing, printing two-up or in landscape mode insteadof portrait mode according to settings in the printer driver. However,the current method can also be practiced in these systems with onlyminor modifications to the document database to allow for multipledocument pages to be associated with a single printed instance.

Finally, the present method was described with reference to a digitalphotocopier system. It is equally feasible to use other multifunctiondevices, such as integrated inkjet multi-function printers, or toimplement the described method in a system where the printer and theoutput scanner are physically distinct devices.

INDUSTRIAL APPLICABILITY

The described method is applicable to the printing, imaging, datamanagement and data processing industries.

1. A computer implemented method of identifying a printed page from ascan of the printed page, the method being executed by a processor withat least a database, the comprising the steps of: generating a page keyof the printed page on the basis of the scan; sending the generated pagekey to the database to initiate a search for a similar page key; and foreach found similar page key: retrieving from the database an instancekey location for a page instance with the respective similar page key;generating an instance key for the printed page, based on the retrievedinstance key location of the respective page instance; and sending thegenerated instance key for the printed page to the database for acomparison with an instance key of the respective page instance, whereina match between the instance keys indicates that the printed page is therespective page instance.
 2. The method of claim 1, wherein the page keyis associated with an image content of the printed page.
 3. The methodof claim 1, wherein the page key is associated with a logical content ofthe printed page.
 4. The method of claim 1 wherein said instance key isassociated with physical characteristic generated by the printingprocess.
 5. The method of claim 1 wherein said instance key is acharacteristic of said physical medium of the printed page.
 6. Themethod of claim 1, wherein the method further includes the step ofretrieving metadata for the respective page instance with a matchinginstance key.
 7. A computer implemented method for identifying a pageinstance of a source document from a scan of said page instance, thescan being obtained from a print of the page instance, the print beingeffected by a printing device on a physical medium, the method beingperformed by a processor in association with a database, the methodcomprising the steps of finding at least one image in the database thatis similar to the scanned image of the printed page instance, thesimilarity being based on a first physical characteristic captured insaid scan, said characteristic being substantially invariant betweendifferent printed instances of said source document; and for each of theat least one similar images: determining a location in the scan based oninformation associated with the respective similar image; obtaining asecond characteristic from said scan, said second characteristics beingpositioned in said location, wherein said second characteristic issubstantially variant between different instances of said sourcedocument; and comparing the second characteristic of the page instancewith a corresponding second characteristics of the respective similarimage, wherein a match between the second characteristics indicates thatthe respective similar image is a source document for the printed pageinstance.
 8. The method of claim 7 wherein said second physicalcharacteristic is associated with the printing of the page instance bythe printing device on the physical medium.
 9. The method of claim 7wherein said second physical characteristic is a characteristic of saidphysical medium.
 10. The method of claim 7, wherein the method furtherincludes the step of retrieving metadata for the source document with amatching instance key.
 11. A method of identifying a printed page, themethod comprising the steps of: scanning a plurality of first printedpages to generate a first scan of each first printed page; generating apage key and an instance key for each first printed page on the basis ofits respective first scan; storing the generated page key and aninstance key for each first page in a database; scanning an unidentifiedprinted page to generate a scan of the unidentified page; on the basisof the scan of the unidentified page, generating a page key of theunidentified printed page; sending the generated page key to thedatabase to initiate a search for a similar page key to the page key ofthe unidentified page; and for each found similar page key: retrievingfrom the database an instance key location for a first page with therespective similar page key; generating an instance key for theunidentified printed page, based on the retrieved instance key locationof the respective first page; and sending the generated instance key forthe unidentified printed page to the database for comparison with aninstance key of the respective first page, wherein a match between theinstance keys indicates that the unidentified printed page is identicalto the respective first printed page.
 12. The method of claim 11,wherein the instance key is selected to be in a location of the pagewith the highest average luminance value.
 13. The method of claim 11,wherein the instance key is selected to be in a location of the pagewith the highest gradient entropy.
 14. The method of claim 11, whereinthe page key is associated with an image content of the printed page.15. The method of claim 11, wherein the page key is associated with alogical content of the printed page.
 16. The method of claim 11, whereinsaid instance key is associated with physical characteristic generatedby the printing process.
 17. The method of claim 11, wherein saidinstance key is a characteristic of said physical medium of the printedpage.
 18. The method of claim 11, wherein the method further includesthe step of retrieving metadata for the respective first page with amatching instance key.
 19. A system for identifying a printed page froma scan of the printed page, said system comprising: an interface for;receiving the scan of the printed page; accessing a database; andcommunicating with imaging means; and a processor for: generating a pagekey of the printed page on the basis of the received scan; sending thegenerated page key to a database to initiate a search for a similar pagekey; and for each found similar page key; retrieving from the databasean instance key location for a page instance with the respective similarpage key; using the imaging means for generating an instance key for theprinted page, based on the retrieved instance key location of therespective page instance; and effecting the sending of the generatedinstance key for the printed page to the database for comparison withthe an instance key of the respective page instance, wherein a matchbetween the instance keys indicates that the printed page is therespective page instance.
 20. A computer readable storage medium havinga computer program recorded thereon, the program being executable by acomputer system to make the computer system identify a printed page froma scan of the printed page, said program comprising: code for generatinga page key of the printed page on the basis of the scan; code forsending the generated page key to a database to initiate a search for asimilar page key; and code for effecting, for each retrieved similarpage key: retrieval from the database art instance key location for apage instance with the respective similar page key; generation of aninstance key for the printed page, based on the retrieved instance keylocation; and sending the generated instance key for the printed page tothe database for comparison with an instance key of the respective pageinstance, wherein a match between the instance keys indicates that theprinted page is the page instance.